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arXiv 1404.7280cond-mat.mtrl-sciphysics.chem-ph
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质子在充水碳纳米管和液态水中的输运性质

Nature of proton transport in a water-filled carbon nanotube and in liquid water

Ji Chen, Xin-Zheng Li, Qianfan Zhang, Angelos Michaelides, Enge Wang

摘要:

用从头算路径积分分子动力学(PIMD)方法研究了质子在液态水和碳纳米管中的输运。在每种情况下,当量子核效应(QNEs)被占观察到的无势垒质子转移。这两个系统之间的关键区别在于,在纳米管中,通过水分子的有利预对准来促进简易PT,而在本体液体中,在PT之前需要水溶剂重组。量子过剩质子在几个相邻的水分子上离域,以及不同水合状态之间的连续相互转换,这表明,与液态水一样,限制下的水合质子最好描述为流动缺陷,而不是任何单独的理想化水合状态,如Zundel,Eigen或所谓的线性H7O3+复合物。这些发现突出了QNE在中等强度氢键(HB)中的重要性,并解释了为什么H+通过纳米通道的扩散受到的阻碍比其他阳离子少得多。

英文摘要:

Proton transport (PT) in bulk liquid water and within a thin water-filled carbon nanotube has been examined with ab initio pathintegral molecular dynamics (PIMD). Barrierless proton transfer is observed in each case when quantum nuclear effects (QNEs) are accounted for. The key difference between the two systems is that in the nanotube facile PT is facilitated by a favorable prealignment of water molecules, whereas in bulk liquid water solvent reorganization is required prior to PT. Configurations where the quantum excess proton is delocalized over several adjacent water molecules along with continuous interconversion between different hydration states reveals that, as in liquid water, the hydrated proton under confinement is best described as a fluxional defect, rather than any individual idealized hydration state such as Zundel, Eigen, or the so-called linear H7O3+ complex along the water chain. These findings highlight the importance of QNEs in intermediate strength hydrogen bonds (HBs) and explain why H+ diffusion through nanochannels is impeded much less than other cations.

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